The present invention relates t a radar arrangement which is particularly intended for measuring the velocity "v" of an object. The arrangement comprises a first receiver and a second receiver which are a distance "d" apart and are in line with the direction of the velocity to be measured and have been provided to receive the waves coming from a high-frequency signal generator after being reflected by the object. The arrangement also comprises a correlator to determine the delay ".tau." of the output signals of the second receiver with respect to the output signals of the first receiver, the correlation being at a maximum for this delay, and an output circuit which processes the velocity information by determining the quantity d/.tau..
An important use of this arrangement is the measurement of the horizontal velocity of an aircraft; in that case the radar arrangement is installed on board the aircraft and the relevant object is the ground.
U.S. Pat. No. 4,041,293 discloses an arrangement of this type. In the arrangement described in this United States Patent a generator is used which transmits a signal with a fixed frequency. At certain distances between the arrangement and the ground and for particular profiles of the ground the received waves may be so weak that it is impossible to process the signals at the outputs of the receiving means. It is then not possible to measure the velocity. This known arrangement is therefore not suitable for the contemplated use for which a continuous and reliable measurement of the velocity is a requirement.